Known devices make it possible, by means of suitable sensors, to measure a wide variety of properties on, for example, a continuously moved yarn. Since the aim is to achieve increasingly higher outputs, the tendency is to produce or test the yarn more rapidly. The yarn is therefore also to pass more rapidly through subsequent processing stages or tests in the laboratory. At high speeds, it becomes increasingly more difficult for conventional sensors to record even irregularities of small extent reliably on the running yarn. The quality of recording of the individual irregularities is therefore impaired.
To raise the monitoring quality, it is conceivable to employ sensors which can supply more comprehensive information on irregularities. One example of such a sensor is a television camera with following image processing which, indeed, not only makes the irregularity recognizable per se, but can also give particulars on the nature of the irregularity. However, for a fast-running yarn which is moved at a speed of 400 m/min and which is recorded by a television camera working at a clock frequency of 50 Hz, this means that the recorded fields show yarn portions which are 130 mm apart. Reckoning on a field resolution of 160 lines, this results in a resolution limit of 0.8 mm on the yarn. This is insufficient for exact analysis of the yarn. If a special camera with a higher frame rate is used, the resolution limit is thereby improved, but the computing complexity during image processing also rises considerably as a result. The sufficiently high-performance special hardware necessary for this purpose must be aimed at the immediate problem to be observed, which also means that this hardware is inflexible. This difficulty could be overcome by no longer aiming to ensure uninterrupted monitoring of the yarn. In that case, although there is very good recording of the yarn properties on specific portions, there is nevertheless no longer any monitoring at all on other portions.